1. Field of the Invention
The present invention relates to a pressure plate assembly, especially for a motor vehicle friction clutch with automatic wear compensation. The pressure plate assembly includes a housing, that is connected or connectable to a flywheel for rotation therewith about a rotational axis. A pressure plate is connected to the housing in rotation-proof fashion, but is axially movable relative to the housing. The pressure plate has a friction surface to support the friction linings of a clutch disk that can be clamped between the flywheel and the pressure plate. The pressure plate assembly also includes an energy storage device, especially a diaphragm spring, a spring force of which acts between the housing and the pressure plate for biasing the pressure plate in the direction of an engaged position of the clutch, whereby the energy storage device acts on the pressure plate via a wear compensation device which is mounted intermediate the pressure plate and the energy storage device. The pressure plate assembly further comprises at least one clearance indicator arranged on the pressure plate having an activating lever section that interacts with the wear compensation device, and a wear detection section that penetrates a substantially axial opening in the pressure plate and interacts, preferably, directly with the flywheel for the purpose of detecting wear, the clearance indicator being axially movable in the opening relative to the pressure plate. The pressure plate assembly also comprises at least one bias element for producing a force action to press the clearance indicator to axially fix the clearance indicator relative to the pressure plate in the friction clamping seat in the opening in the pressure plate.
2. Description of the Related Art
A prior art pressure plate assembly of this type is known, for example, from DE 4306688 A1. In this prior art pressure plate assembly, a helical compression spring acts between a free end of the wear detection section of the clearance indicator and the pressure plate. The helical compression spring is arranged so that a spring pressure force of the spring is inclined, relative to a longitudinal axis of the opening in the pressure plate and thus relative to a longitudinal axis of the wear detection section of the clearance indicator. As a result, a tilting moment is produced on the wear detection section around an axis located at a right angle to its longitudinal axis, creating a friction clamping seat for the wear detection section in the opening. To avoid impairing the axial mobility of the clearance indicator (i.e., of the wear detection section) when wear occurs, the spring pressure force provided by the helical compression spring must be relatively slight. However, this means that the friction clamping force exercised by the inclined spring is also limited.
During the operation of motor vehicle friction clutches that have clearance indicators of this type, vibrations can occur that, if located in the resonance vibration range of the clearance indicator, may cause the clearance indicator to vibrate and thus lead to the short-term release of the friction clamping seat. For this reason, the helical compression spring must also exercise an axial force component on the clearance indicator. If, in the absence of an axial propellant force, the clearance indicator is moved in the axial direction by the movement or vibration of the clutch during the brief release of the friction clamping seat, and particularly if the indicator is moved away from the flywheel, the indicator will not correctly detect wear. The helical compression spring thus has a double function. First, it produces the tilting moment. Second, it provides an axial bias for the clearance indicator toward the flywheel.